Motor vehicles such as dump trucks, refuse trucks, transit concrete mixing trucks, open-bed trucks, utility trucks, military trucks and other vehicles of various types to which a significant load may be added for transport are limited in their load transporting ability by various factors. Such as the weight bearing capacity of their supporting axles and applicable federal and state law. With such laws for example limiting the gross vehicle weight to 80,000 pounds, the weight carried by a single axle to 20,000 pounds and there being an exception as to consecutive axles that limits them to carrying a prescribed combined weight depending on their number and spacing. For example, the combined axle carrying weight is limited to 34,000 pounds in regard to the two powered tandem axles that are typically employed with heavy-duty load-transporting motor vehicles. And with such factors as a result impacting the use of such motor vehicles in that the more weight the vehicle can transport at a time, the more useful the vehicle can be provided other factors that impact the ability of the vehicle to perform in an acceptable manner are also taken into account. With such factors including the axle manufacturers rated load capacity.
And in regard to such motor vehicles where it is desired to increase their load carrying capacity within the prescribed limits, it is common practice to provide one or more auxiliary axles that are deployed on command to help support the motor vehicle and thereby reduce the weight carried by the axles that normally support the vehicle. Wherein the axles that normally support the vehicle are then referred to as primary axles and include at least one axle with steerable wheels and one or more powered axles with wheels. And the auxiliary axles are referred to as either a pusher axle, tag axle or trailing axle in distinguishing between where and how they are employed to help support the motor vehicle. Wherein a pusher axle is suspended from the motor vehicle chassis in a location to operate between a forwardly-located primary axle with steerable wheels under the control of the vehicle operator and one or more rearwardly-located primary axles with powered wheels. Whereas a tag axle is suspended from the motor vehicle chassis to operate rearward of one or more primary axles with powered wheels but not normally at any substantial distance behind the motor vehicle chassis. And a trailing axle (that has also been referred to as a tag axle and trailing tag axle) is also suspended from the motor vehicle chassis but in a manner to operate at a substantial distance rearward of the motor vehicle chassis.
In the case of a motor vehicle equipped with a trailing axle, when not in use the trailing axle is typically stowed at a location near or above the highest point of the payload-carrying body, so as to not interfere with the normal operation of the latter. For example, a dump truck equipped with a trailing axle will typically stow the trailing axle above the rear of the dump body so that the payload can be dumped without interference from the trailing axle and its wheels. And to provide for such, the trailing axle suspension system is typically comprised of a pair of suspension arms that are pivotally attached to the motor vehicle chassis and are swung to establish the trailing axle in a stowed condition on the dump body and in a deployed condition to help support the truck chassis from behind with the trailing axle. And in addition to this trailing axle movement via the swing of the suspension arms, trailing axles will often require a secondary movement relative to these suspension arms to further stow the axle in a more acceptable or desirable location and compact manner. And again using a dump truck equipped with a trailing axle as an example, the trailing axle with its wheels will often exceed vehicle height restrictions when these suspension arms are swung to establish the trailing axle and its wheels in the stowed position and thus the trailing axle with its wheels often requires further movement relative to these suspension arms in order to comply with height restrictions and so that the dump body can be operated in the desired manner when the trailing axle is not being used.
Various approaches directed at providing a suitable trailing axle suspension system addressing the above needs are for example disclosed in U.S. Pat. No. 5,823,629, U.S. Pat. No. 6,247,712 and U.S. Pat. No. 7,775,308. And in these and other approaches that have addressed such needs, the trailing axle is typically supported for swinging movement relative to the suspension arms pivotally connected to the motor vehicle chassis by a cross-member rigidly joining the suspension arms and wherein an actuator operating between the trailing axle and this cross-member is employed to establish their angular relationship in both the stowed and deployed condition of the trailing axle. And when the trailing axle is deployed and forced to help support the motor vehicle chassis in the deployed condition, all of this force is transmitted through this cross-member to these suspension arms and thereby to the motor vehicle chassis. Moreover, this cross-member is also subjected to torque with the trailing axle in the deployed condition and this results in torsion stresses also being transmitted to this cross-member and being magnified and concentrated at the ends of this cross-member where it joins the suspension arms. And thus requires the cross-member being adequately structurally suited to the task and preferably without significantly adding to its weight. As the motor vehicles that benefit from a trailing axle are generally of the payload-carrying type and payload-carrying vehicles desire minimal vehicle weight in order to maximize the payloads they can carry and that includes the weight added with a trailing axle installation.